1. Field of the Invention
The present invention relates to a biochemical sensor, particularly to a light-assisted biochemical sensor based on a light addressable potentiometric sensor.
2. Description of the Related Art
Refer to FIG. 1. The light addressable potentiometric sensor (LAPS) is a biochemical sensor based on the photovoltaic effect of semiconductor.
FIG. 1 is a diagram schematically showing the pH measurement system of the traditional light addressable potentiometric sensor. The LAPS mainly comprises a semiconductor substrate 101, and an oxide layer 102 or a nitride layer formed on the semiconductor substrate 101. An external light source 104 is located behind the back surface of the semiconductor substrate 101. When a light with a wavelength is emitted to a semiconductor, the semiconductor absorbs the photons such that the jumping of atoms from valance band to the conduction band will produce pairs of electrons and holes. In general, the electron-hole pair will be rapidly recombined, and then the current can not be detected by an external circuit. If the LAPS is biased at a reversed bias (N-type silicon is biased at a negative voltage and P-type silicon is biased at a positive voltage), a depletion region is generated in the semiconductor, and the electron-hole pair close to the depletion region is separated to the two sides of the depletion region before they have a chance to recombine with each other. If the intensity-adjusting light source is used to illuminate the light, the alternate variations of the electron-hole pair will occur. Then, the photocurrent is detected in the external circuit. The photocurrent variations correspond to the responses of the sensing region of the LAPS. As a result, the specific ion concentration or the biological substance concentration of an electrolyte is detected by the photocurrent variation due to the potential variation of the sensing region.
Since the LAPS can continuously detect a plurality of parameters and have the advantages of high sensitivity, high stability, and high input resistance, the application range thereof is very wide. However, the traditional LAPS detects the electrolyte concentration in cooperation with the external light source, whereby the measurement system of the LAPS has larger volume and the measuring process is more complicated. These disadvantages limit the convenience and practicability of the LAPS.